The present invention relates to document print job encryption, and in particular, to a method, and to a print job data file resulting from implementation of that method, whereby post-rendering analyses of the job's encrypted print stream can take place without revealing the substantive content of the print job per se.
Typically, a document print job is secured by encrypting the related PDL data such that if it is intercepted, as it may be, between the host and the intended recipient printing (imaging) device, it cannot be interpreted, viewed or printed in any unauthorized manner. However, it is also typical that the manner in which such PDL data is encrypted results in an attempted post-rendering analysis process, such as a process involving job auditing, job accounting, and job splitting, failing because of the fact that the analysis process itself, in order to succeed, needs to have access to certain non-substantive content data which it cannot get because of the overall and generalized encryption which has previously taken place.
Various approaches to encryption so far have not offered a satisfactory way to assure secure encryption only of substantive content materials, while leaving other print job data file information generally accessible for post-rendering analyses of the types generally suggested above, as well as others.
The present invention addresses this issue in a very complete and satisfactory way by proposing an encryption methodology whereby a document print job data stream is segmented appropriately to allow for encryption to take place at essentially all regions other than those which preferably should remain accessible for various post-rendering processes/analyses. Fundamentally, practice of the present invention, in its preferred and best-mode form, features a method for encrypting a document print job including the steps of (a) identifying and individuating, within such a job, the so-called content commands as distinguished from the non-content commands associated with the job, and (b) as a consequence of that identifying and individuating practice, encrypting only data that is contained within the content commands. This approach will, in most instances, yield an encrypted print job data stream whose relevant non-substantive contents will be fully accessible and available for all expected post-rendering processes and analyses.
Another approach to implementing the invention, which deals with a document print job data stream with an even smaller, or finer, degree of treatment granularity, involves recognizing that the content commands themselves typically include both non-content fields and content fields. In this practice of the invention, encryption only takes place with respect to such content fields, thus leaving the remainder of the entirety of the associated print job data stream accessible to post-rendering processes and analyses.
Provided immediately below is a hierarchical, textual representation of the typical architecture of a document print-job in relation to the make-up of page instructions for a given page in the associated document.                I. Page Instructions                    A. Non-content commands—no ink-on-paper            B. Content commands—ink-on-paper                            (1) Non-content fields                (2) Content fields                                                
Page non-content commands do not cause “ink-on-paper”. Typical of such commands are (a) the number of copies per page, (b) page orientation, (c) cursor position, and (d) pen color. Page content commands do cause ink-on-paper, and include, as above indicated, both non-content fields and content fields. Illustrations of non-content fields include (a) command opcode, (b) length of command operand, and (c) command delimiter. An illustration of a content field is a command operand itself.
The above-mentioned and other features and advantages of the present invention will become more fully apparent as the detailed description below is read in conjunction with the accompanying drawings.